Nandi J, Ray T K
Biochem J. 1987 Jan 1;241(1):175-81. doi: 10.1042/bj2410175.
The effect of nolinium bromide [2-(3,4-dichlorophenylamino)quinolizium bromide], which acts as a K+ antagonist in the gastric H+ +K+-dependent ATPase reaction, was investigated at the level of 32P-labelled intermediates of the gastric ATPase reaction. A concentration-dependent effect of nolinium bromide was observed on the concentrations of phosphorylated intermediates. At low (up to 50 microM) concentrations the drug did not interfere with the concentrations of intermediates but exhibited a competition with K+ at the level of both 32P-labelled intermediates and hydrolysis of ATP at pH 7.0. Similar competition was noted in the H+ +K+-dependent ATPase reaction. Low nolinium bromide concentrations also drastically slowed the enzyme turnover. The concentrations of the intermediates were lowered appreciably between 50 microM- and 100 microM-nolinium bromide without affecting the ATP hydrolysis, and the effects were independent of pH. Similar to the effects at pH 7.0, the drug also exhibited competition with K+ in lowering the E approximately P concentration at pH 5.0. A dramatic effect of pH on the K+-sensitivity as well as on turnover of the 32P-labelled intermediates was observed. Although the concentrations of intermediates remained nearly unaltered at various pH values, the K+-stimulated hydrolysis of ATP showed an optimum at pH 7.0 with sharp declines at pH 5 and 8. The data suggest a critical involvement of H+ in the conversion of the K+-insensitive E1 approximately P into the K+-sensitive E2 approximately P form of the enzyme. Nolinium bromide appears to function as a K+ analogue and seems to block the entry of K+ at the K X E2 step, thereby interfering with the enzyme turnover.
研究了在胃ATP酶反应的32P标记中间体水平上，作为胃H⁺ +K⁺依赖性ATP酶反应中K⁺拮抗剂的溴诺林（2-(3,4-二氯苯基氨基)喹嗪溴化物）的作用。观察到溴诺林对磷酸化中间体浓度有浓度依赖性影响。在低浓度（高达50微摩尔）时，该药物不干扰中间体浓度，但在32P标记中间体水平以及pH 7.0时ATP水解方面表现出与K⁺的竞争。在H⁺ +K⁺依赖性ATP酶反应中也观察到类似的竞争。低浓度的溴诺林也显著减缓了酶的周转。在50微摩尔至100微摩尔溴诺林之间，中间体浓度明显降低，而不影响ATP水解，且这些影响与pH无关。与pH 7.0时的作用类似，该药物在pH 5.0时降低E≈P浓度方面也表现出与K⁺的竞争。观察到pH对32P标记中间体的K⁺敏感性以及周转有显著影响。尽管在不同pH值下中间体浓度几乎保持不变，但K⁺刺激的ATP水解在pH 7.0时显示出最佳值，在pH 5和8时急剧下降。数据表明H⁺在将酶的K⁺不敏感E1≈P形式转化为K⁺敏感E2≈P形式中起关键作用。溴诺林似乎作为K⁺类似物起作用，似乎在K×E2步骤阻断K⁺的进入，从而干扰酶的周转。
